1. Field of the Invention
Embodiments of the present invention generally relate to a method and apparatus for pulse width modulation generation.
2. Description of the Related Art
Distributed power systems typically comprise a power source that generates direct current (DC) power, a power converter, and a controller. The power source may be a solar panel or solar panel array, a wind turbine or a wind turbine array, a hydroelectric generator, fuel cell, and the like. The power converter converts the DC power into alternating current (AC) power, which may be coupled directly to the AC power grid. The controller monitors and controls the power sources and/or power converter to ensure that the power conversion process operates as efficiently as possible.
One type of power converter is known as a micro-inverter. Micro-inverters typically convert DC power to AC power at the power source. Thus, each power source is typically coupled to a single micro-inverter such that multiple micro-inverters provide power to the AC power grid. It is critical that the AC power generated is effectively converted to match the intended load, the AC grid. Control of the micro-inverters can grow complex with the switching transistors and consume power that could otherwise be beneficially contributed to the AC power grid as the number of power sources (and micro-inverters) increase within a large power generation array.
In addition, for higher power applications, multi-level converter topologies are applied to efficiently provide power from power sources. Multi-Level Inverters reduce the total output LC (Inductor/Capacitor) filter size by a factor of N2 compared to a conventional (2 or 3 level) inverter, where N represents the number of levels.
A newer class of converter that combines the modularity of a micro-inverter with a multi-level converter has recently gained academic attention. This architecture effectively splits the output filter to be distributed over the N micro-inverters creating an even further size reduction, resulting in the size of the output LC filter becoming trivial for series-connected micro-inverters employing a system multi-level architecture. However, with this architecture, the PWM switching of the series-connected micro-inverters must be synchronized and if the micro-inverters lost the synchronization at the PWM switching frequency then the resulting system currents would destroy the switching transistors in the micro-inverters.
Therefore, there is a need in the art for a simplified distributed power coordination system without a global controller and control bus during the conversion of DC power to AC power for the power grid.